我有一个使用RxJava和Retrofit2加载数据的Activity。为了防止每次发生配置更改时都触发请求,我使用了cache()
操作符。这工作得很好,我可以看到请求只发出一次。问题是,我需要不时地发出新的请求来获取新的数据。换句话说,我需要使缓存无效。我该怎么做呢?
活动正在使用存储库发出请求:
public class Repository {
private final PlaceholderApi api;
private Observable<List<Post>> obs;
private static Repository inst;
public static Repository instance() {
if (inst == null) {
inst = new Repository();
}
return inst;
}
private Repository() {
HttpLoggingInterceptor logging = new HttpLoggingInterceptor(message -> System.out.println(message));
logging.setLevel(HttpLoggingInterceptor.Level.BASIC);
OkHttpClient okhttp = new OkHttpClient.Builder()
.addInterceptor(logging)
.build();
Retrofit retrofit = new Retrofit.Builder()
.client(okhttp)
.addConverterFactory(MoshiConverterFactory.create())
.baseUrl("http://jsonplaceholder.typicode.com/")
.addCallAdapterFactory(RxJavaCallAdapterFactory.createWithScheduler(Schedulers.io()))
.build();
api = retrofit.create(PlaceholderApi.class);
}
public Observable<List<Post>> getAll() {
if (obs == null) {
obs = api.getPosts().cache();
}
return obs;
}
}
活动代码:
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private Subscription sub1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
sub1 = Repository.instance().getAll().subscribe(/* handle posts list */);
}
@Override
protected void onDestroy() {
super.onDestroy();
if (sub1 != null && !sub1.isUnsubscribed()) {
sub1.unsubscribe();
}
}
}
下面是一个使用OnSubscribeRefreshingCache包装器类的例子,来自Dave Moten的回答:
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private Subscription sub1;
private OnSubscribeRefreshingCache<List<Post>> postCache;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
postCache = new OnSubscribeRefreshingCache(Repository.instance().getAll());
sub1 = subscribe(Observable.create(postCache));
}
@Override
protected void onDestroy() {
super.onDestroy();
if (sub1 != null && !sub1.isUnsubscribed()) {
sub1.unsubscribe();
}
}
private Subscription subscribe(Observable<List<Post> postObservable){
return postObservable.subscribe(/* handle posts list */);
}
private void invalidateCache(){
postCache.reset();
sub1 = subscribe(Observable.create(postCache));
}
}
然后在Activity生命周期方法中调用invalidateCache()
方法或任何适合您的方法。
另一种解决问题的方法是使用OperatorFreeze(没有操作符缓存),如果你使用持久呈现器。这个操作符可以在配置发生变化时暂停你的Observable,并在activity重新创建时恢复它。你也不需要在存储库中存储observable